Improve peer connection handling

[peterargue]

This PR was originaly submitted to ipfs/go-bitswap#590

Currently, the bitswap network only adds peers to its client/server peer lists that connected after the network has started. This means the network must be started before enabling the libp2p listeners, otherwise some peers may connect too early and never be added to the network.

To address this, this PR updates the bitswap network's Start() method to first, listen for new peer connection events, and then iterate through all peers and add any that support the bitswap protocols. The issue and solution were originally described by @Stebalien in #83.

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[peterargue]

Hey @Jorropo, I ported this change over.

[Stebalien]

This will race with the "old" version of notifications. Instead, we need to:

1. Drop the old version (the net notifiee).
2. Subscribe to EvtPeerConnectednessChanged to get connectivity changes.
3. We care about "disconnected" events, but ignore "connected" events. Instead, rely on "protocol changed" and "identify" notifications to tell you that the peer supports bitswap (but check this with @Jorropo).

[Stebalien]

Ah, but once you do this, you also have to move the existing connection walk to the top of this function. That is, you need to:

1. Subscribe to connect/disconnect events.
2. Process all existing connections.
3. Start processing the events.

Failure modes:

• If you do 2 before 1, you could miss new connections.
• If you do 3 concurrent with 2, you could process a connect/disconnect event in step-3, then re-add the peer in the step-2 loop.

If you do them in order (1,2,3), you may end up processing a "connect" event for a disconnected peer in step 3, but then you'll process the disconnect event.

You could additionally check the peer's "connectedness" before updating a peer's status, but I don't think that is necessary.

[Stebalien]

Hm. Although, I think we need to ask libp2p for all connections to the peer to make sure that we have a non-transient one. I wonder if that'll cause any issues? I assume we'll re-identify when we create a new connection... That'll require some testing.

Ideally libp2p would let us filter protocols by connection type, but that's a larger change.

Thoughts @Jorropo? @aschmahmann?

[Stebalien]

I've filed two related libp2p issues:

• Add Transient as a "connectedness" state libp2p/go-libp2p#2692 (easier, but may cause unexpected issues).
• Per-connection protocol list libp2p/go-libp2p#2693 (harder, but highly desirable and is likely to fix hidden issues and simplify quite a bit of code just about everywhere).

[codecov]

Codecov Report

Attention: Patch coverage is 73.33333% with 16 lines in your changes are missing coverage. Please review.

Project coverage is 65.48%. Comparing base (79cb4e2) to head (decd8d9).
Report is 23 commits behind head on main.

❗ Current head decd8d9 differs from pull request most recent head a8040f8. Consider uploading reports for the commit a8040f8 to get more accurate results

@@            Coverage Diff             @@
##             main     #526      +/-   ##
==========================================
- Coverage   65.56%   65.48%   -0.08%     
==========================================
  Files         207      204       -3     
  Lines       25597    25588       -9     
==========================================
- Hits        16782    16756      -26     
- Misses       7336     7351      +15     
- Partials     1479     1481       +2     

Files	Coverage Δ
bitswap/network/ipfs_impl.go	74.70% <73.33%> (+0.23%)	⬆️

... and 18 files with indirect coverage changes

[Stebalien]

I believe libp2p/go-libp2p#2696 should unblock this from the libp2p side.

[peterargue]

@Jorropo any chance you can take a look and provide any remaining feedback?

[lidel]

Triage notes:

• unsure if this is still needed, Add Transient as a "connectedness" state libp2p/go-libp2p#2692 landed, and the stack is being refactored (e.g. chore: fix connectedness libp2p/go-libp2p-kad-dht#976) to take advantage of it
  • thoughts @sukunrt @MarcoPolo @2color?